Zeolites are well known adsorbents, which have been used between glass panes, either alone or in a sealant. The zeolite is disposed along the periphery of the space enclosed by the panes, and the zeolite adsorbs water vapor from the space between the panes. Zeolite functions as a "molecular sieve". Specifically, zeolite has pores into which the material being adsorbed passes. The pores have apertures of a size sufficient to pass the molecules of the material being adsorbed but small enough to block materials not adsorbed. U.S. Pat. Nos. 4,151,690, 4,141,186 and 4,144,196 disclose such molecular sieve zeolites.
Known zeolites have pore aperture sizes of 3 to 10 angstroms. However, zeolites with aperture sizes 4 angstroms or greater, when used in an insulating window, adsorb gaseous components in the air space, such as oxygen and nitrogen, as well as the water vapor which is desired to be adsorbed. These zeolites then outgas the oxygen and nitrogen when the temperature rises or the pressure lowers. These zeolites, when used in a sealant between glass panes in a window, adsorb the oxygen and nitrogen when cooled (as during night) and then release the gases when the glass is heated (as during the day). This causes large pressure variations in the enclosed air space, which can lead to problems with the windows such as excessive deflection or inflection. This outgassing can also lead to a loss of adhesion between the glass panes and the sealant because agglomeration of the gases permits small bubbles to form which migrate to the adhesive interface.
U.S. Pat. Nos. 4,144,186 and 4,144,196 attempt to solve this problem by using zeolite adsorbents with pore apertures of 3 angstroms or less in size so that oxygen and nitrogen molecules cannot enter into the pores, thus preventing the adsorption and the desorption of these gases. U.S. Pat. No. 4,151,690 contemplates the use of zeolite adsorbents with larger pore aperture sizes, which have been pretreated by preadsorption of a low molecular weight polar material to partially suppress the undesirable adsorption of the gases.